This invention relates generally to workpiece shuttle mechanisms such as are found on machine tools and more specifically, this invention relates to an improved workpiece shuttle mechanism which is operative to store a plurality of workpiece carrying pallets and to shuttle a workpiece carrying pallet then at a selected storage location to the worktable of a machine tool or to shuttle the workpiece carrying pallet then on the machine tool to a storage location.
As conventional, manually operated, drilling and milling machines are being superseded by sophisticated computer numerically controlled machining centers which are capable of automatically performing a sequence of different machining operations on the workpiece without human intervention, the need to rapidly and efficiently shuttle parts onto and off of the machine tool is becoming increasingly more important. Because of the relatively large capital cost of such sophisticated numerically controlled machine tools, it is imperative that the then-completed workpiece on the machine tool table be interchanged as quickly as possible with an unfinished workpiece upon completion of the sequence of machining operations so that machine idle time can be kept at a minimum. By reducing machine idle time, machine productivity, that is the number of parts that can be machined during any given time, is maximized.
In the past, rapid and efficient interchange of workpieces has been achieved by equipping the computer numerically controlled (CNC) machining center with a workpiece changer or pallet shuttle mechanism which automatically interchanges the pallet carrying then-completed workpiece with a pallet carrying an unfinished workpiece after completion of the sequence of machining operations. Examples of prior art workpiece changers and shuttle mechanisms may be found in U.S. Pat. No. 3,825,245 issued on July 24, 1974 to John G. Osburn et al and U.S. Pat. No. 4,133,423 issued on Jan. 9, 1979 to Frank Zankl. Each of the above listed patents describes an apparatus for completing a single interchange of the workpiece then on the machine tool table with an unfinished workpiece stored on a single storage shuttle or table. Once an interchange has been completed between the then-completed workpiece on the machine tool table and the unfinished workpiece at the storage shuttle, then the now-completed workpiece on the storage shuttle must be manually replaced by the operator with an unfinished workpiece to enable a subsequent exchange by the workpiece changer when the now-unfinished workpiece on the machine tool table is machined.
The obvious drawback of such workpiece changer devices is that only one unfinished workpiece is stored by the workpiece changer so that even though interchange between a then-completed workpiece on the machine tool table with an unfinished workpiece on the workpiece changer shuttle can be accomplished quite rapidly and efficiently, human effort is still required to load and unload the workpiece changer shuttle. In an effort to reduce the frequency of manual part loading and unloading to enable relatively long periods (8-10 hrs.) of unattended machine tool operation, a pallet storage magazine and associated shuttle mechanism has been developed to enable multiple storage of unfinished and finished workpiece carrying pallets. Such a pallet storage magazine and shuttle mechanism comprises a conveyor which rotates on a base located adjacent to the machine tool bed. A plurality of pairs of pallet receiving and storage guides are fastened on the conveyor in spaced apart relationship so that each of the guides of each pair are parallel to each other. The conveyor rotates about two centrally located oppositely extending shuttle arms which are each extended and retracted by a hydraulic cylinder. Each shuttle arm has a "T" shaped finger at its distal end for mating with a complementary slot on each workpiece carrying pallet when, following arm extension, the arm is rocked by a tilting mechanism to locate the finger in the pallet slot.
While the above-described pallet storage magazine and shuttle mechanism enables multiple pallet storage in contrast to the prior art workpiece shuttle mechanisms described earlier, it is nonetheless subject to the disadvantage that two mechanisms must be provided, one to extend and retract each shuttle arm and the other to rock each shuttle arm to releaseably engage the "T" shaped finger at the distal end of the shuttle arm in the complementary receiving slot on the pallet. In contrast, the present invention concerns an improved workpiece storage and shuttle mechanism which is not subject to the disadvantages of present day pallet storage and shuttle mechanisms.
The principle object of the present invention is to provide a workpiece storage and shuttle mechanism which employs but a single mechanism for releaseably engaging the pallet and for shuttling the workpiece carrying pallet between one of the several storage locations and the machine tool table. By eliminating the need for separate mechanisms for releaseably engaging the pallet carrying workpiece and for shuttling the workpiece between one of the storage locations and the machine tool worktable, fabrication can thus be simplified and fabrication costs can be reduced. Another object of the present invention is to increase the speed at which pallets can be interchanged. Other objects and advantages of the invention will become apparent from the detailed description provided hereinafter.